1. Field of the Invention
The present invention relates to an image processing apparatus for combining images picked up and obtained by moving an image detector, a control method for controlling the image processing apparatus, and a computer-readable storage medium.
2. Description of the Related Art
Japanese Patent Laid-Open Nos. 11-215324 and 2005-326260 disclose a method for forming a high-definition image. In this method, a high-definition image is formed by combining a plurality of images obtained by moving an image detector in a main scanning direction and/or a sub-scanning direction to perform an image pickup operation multiple times at different positions displaced from each other by a distance smaller than a width of one pixel (one pixel width).
For example, as illustrated in FIG. 8, an image detector 810 including a plurality of image pickup elements 801 is moved in a main scanning direction and/or a sub-scanning direction to perform an image pickup operation four times at different positions displaced from each other by a 0.5-pixel width. Then, by properly combining the four images obtained, a high-definition image 820 with a resolution doubled in each scanning direction can be obtained.
An image pickup element having poor output characteristics is often included in an image detector, and is generally referred to as a defective pixel. It is a widespread practice to correct such a defective pixel on the basis of normal pixels therearound. FIG. 9 illustrates the image detector 810 including a defective pixel 901. If a plurality of images picked up by this image detector 810 at different positions displaced from each other by a distance smaller than one pixel width are combined together, the resulting defective pixels 901 are adjacent to each other. As a result, the accuracy of the above-described correction based on normal pixels around a defective pixel will be degraded.
It may be possible to perform defect correction of a plurality of images individually before combining them to form a high-definition image. However, in view of spatial resolution of images, it is apparent that the accuracy of such correction is lower than that of the correction described above.